In many situations there is a requirement for a self-lubricating plain bearing, firstly because a plain bearing is cheap and easy to produce and generally reliable and efficient in operation provided it has sufficient lubrication, and secondly because the self-lubricating facility gives the continued lubrication referred to above as a requirement in a plain bearing, without necessitating dismantling of the bearing.
One form of self-lubricating plain bearing comprises a metal capillary bearing member formed from metal powder with or without graphite by pressing under a high pressure in a mold, followed by sintering in a hydrogen atmosphere. In operation of the bearing the lubricant is sucked out of the pores of the bearing member and supplied to the bearing surface of the sintered member and the shaft, by the rotating shaft, as a result of suction and an increase in temperature, due to capillary action, according to the speed of rotation of the shaft. This arrangement also includes additional lubricant reserve means, for example in the form of a felt ring, deposits of lubricant or grease and the like. It is also necessary to collect lubricant, such as oil, which escapes from the bearing, and felt discs or suitably shaped centrifuging rings are used for this purpose. In a plain bearing of that kind however, there is the danger that a satisfactory film of lubricant may not be formed when the speed of rotation of the shaft is low and also when the shaft is stationary, so that metal-to-metal contact may occur, with evident detriment to the bearing surfaces, whereby the bearing arrangement does not always provide the noise-free and smooth running which is generally a requirement in such bearings.
In other plain bearings of the above-mentioned kind, in the form of kinematic swivel joints, in which the sliding bearing surfaces are of a cylindrical, tapered or spherical configuration, the bearing runs smoothly, but it has to be re-lubricated from time to time in order to maintain the original bearing quality.